The present invention relates to the technical field of a display device comprising a light-emitting element per pixel and an electronic apparatus comprising such display device.
Conventionally, with display devices comprising a light-emitting element per pixel, after a digitized image signal is converted into an analog image signal, such analog image signal is applied to the light-emitting elements.
Here, in order to convert the digital image signal into an analog image signal, it is necessary to utilize a so-called digital/analog converter (hereinafter referred to as a xe2x80x9cD/A converterxe2x80x9d).
As such D/A converter, so-called capacitive D/A converters and so-called resistive D/A converters are known.
Among the above, as the resistive D/A converter, there is a D/A converter utilizing so-called ladder resistance wherein resistors are connected in a ladder shape. As D/A converters utilizing ladder resistance may be integrated easily, they are preferable for being incorporated into an active-matrix type display device.
Nevertheless, in order to realize large driving power upon using a D/A converter utilizing ladder resistance, it is necessary to lower the value of resistance of the respective resistors structuring the D/A converter. Thus, the overall electric power consumption will increase. Particularly in an active-matrix type display device, electric power consumption is severe since D/A converters are necessary per multitude of light-emitting elements.
Moreover, in order to realize large driving power upon using a capacitive D/A converter, it is necessary to increase the capacitance value within the D/A converter. Thus, integration becomes difficult.
The present invention realizes a display device capable of driving light-emitting elements utilizing drive currents having a large current value and lowering electric power consumption by suppressing current consumption, and an electronic apparatus employing such display device.
The display device of the present invention comprises:
a plurality of current-driven light-emitting means respectively contained in a plurality of pixels formed in a matrix shape; and
driving means for converting, by adding a current having a current value corresponding to the digital value contained in the digital data signal, the digital data signal into an analog data signal, applying the analog data signal to the light-emitting means, and driving the light-emitting means.
The plurality of pixels is formed on a substrate, such as a transparent substrate. Thin-film current-driven light-emitting elements (light-emitting elements wherein the luminance degree changes in proportion to the current quantity to be flowed into the diode) may be used as the plurality of light-emitting means.
As the driving means generates an analog data signal by adding a current, the light-emitting means is driven with large driving power and electric power consumption is lowered by the generation of wasteful drive currents being suppressed.
Preferably, the D/A converter includes a current mirror circuit for generating a current having a current value corresponding to the digital value contained in the digital data signal.
More preferably, the current-adding D/A converter includes a current mirror circuit for generating a current having a current quantity corresponding to the digital value contained in the digital data signal. By including a current mirror circuit, the analog data signal may be supplied to the light-emitting means efficiently.
Preferably, the driving means comprises additional-basic-current application means for constantly applying a prescribed additional basic current to the light-emitting means while making the light-emitting means illuminate in correspondence with the digital data signal.
The additional basic current may be a current having a prescribed current quantity set in advance and lower than the minimum current quantity within the range of currents in which the luminance of the light-emitting polymer changes in proportion to the current-luminance property of the light-emitting means.
By constantly applying the additional basic current to the light-emitting means while the light-emitting means is illuminating, the luminance of the light-emitting means will be a luminance in proportion to the current quantity of the analog data signal. Thereby, obtained are images accurately corresponding to the supplied digital data signal.
A display device of the present invention comprises:
a plurality of current-driven light-emitting means respectively contained in a plurality of pixels formed in a matrix shape;
data line driving means for converting, by adding a current having a current value corresponding to the digital value contained in the digital data signal, the digital data signal into an analog data signal, applying the analog data signal to the light-emitting means, and driving the light-emitting means;
a scanning line for supplying a scanning signal;
a data line connected to the data line driving means and for supplying the analog data signal; and
switching means connected to the scanning line, the data line, and the light-emitting means inside the pixel and for applying the analog data signal to the light-emitting means in correspondence with the scanning signal supplied from the scanning line and driving the light-emitting means.
As the data line driving means generates an analog data signal by adding a current, the light-emitting means is driven with a large driving power and electric power consumption is lowered by the generation of wasteful drive currents being suppressed.
By providing a switching means to each light-emitting means, realized is an active-matrix type display device capable of controlling the drive of the light-emitting means for each pixel. Thus, displayed are images of high resolution.
Preferably, the switching means is formed of a thin-film transistor (hereinafter referred to as xe2x80x9cTFTxe2x80x9d); for example, a polysiliconthin-filmtransistor. By employing the polysilicon thin-film transistor, suppressed is the lowering of the driving power pursuant to a long-term flow of strong current.
Preferably, the data line driving means includes a current-adding D/A converter for converting, by adding a current having a current value corresponding to the digital value contained in the digital data signal, the digital data signal into an analog data signal.
More preferably, the D/A converter includes a current mirror circuit for generating a current having a current value corresponding to the digital value contained in the digital data signal. By including a current mirror circuit, the analog data signal may be supplied to the light-emitting means efficiently.
The additional basic current may be a current having a prescribed current quantity set in advance and lower than the minimum current quantity within the range of currents in which the luminance of the light-emitting polymer changes in proportion to the current-luminance property of the light-emitting means.
By constantly applying the additional basic current to the light-emitting means while the light-emitting means is illuminating, the luminance of the light-emitting means will be a luminance in proportion to the current quantity of the analog data signal. Thereby, obtained are images accurately corresponding to the supplied digital data signal.
The light-emitting means of the present invention is preferably formed of a light-emitting polymer. By employing a light-emitting polymer, obtained are images of high intensity.
An electronic apparatus of the present invention comprises the display device of the present invention. Thus, it is possible to display images on the electronic apparatus of the present invention efficiently and with low electric power consumption.